There is an increasing demand in the automobile industry to provide fuel economy and emissions at an affordable cost whilst maintaining customer performance. This is felt very strongly with cabin heater performance where, due to the demand for very high fuel economy from the engine, there is no waste heat left for transfer to the engine coolant for use in a cabin heater. As a consequence auxiliary heaters are being fitted to vehicles. Currently the main type of auxiliary heater is a supplementary electric heater which, while effective in providing customer comfort, does so at a reasonably high cost and poor fuel economy.
To reduce emission from an engine one or more emission control devices such as a catalytic converter may be used to reduce the emissions from the engine. Further, a heat exchanger may be used to cool exhaust gas downstream of a catalyst system and introduce this cooled exhaust gas into the engine before the compressor side of a turbocharged engine. This system is referred to as a Tow Pressure exhaust gas recirculation' and has the advantage of lower emissions and fuel economy than a conventional exhaust gas recirculation (EGR) system. One disadvantage of such a low pressure system is the increased cost associated with the additional heat exchangers, pipework and valves.
One example of a low pressure exhaust gas recirculation system is shown in FIG. 1B. An internal combustion engine 105 has an exhaust manifold 106 to which is connected an exhaust pipe 107u leading to a turbine 81 of a turbocharger for the engine 105. Exhaust gas flows through the turbine into an emission control device 112 such as a catalytic converter and then out via an exhaust pipe 107d. A throttle valve 153 is used to control the flow of air entering the compressor 80. The emission control device 112 is used to reduce the emissions passing out from the engine 105 into the atmosphere via the exhaust pipe 107d. 
A low pressure exhaust gas recirculation system 150 includes an exhaust gas heat exchanger 111 to selectively cool any exhaust gas passing through a conduit 151 of the system 150. The low pressure exhaust gas recirculation system 150 recirculates exhaust gas from a position downstream of the catalyst 112 to a compressor 80 of the turbocharger. A valve 152 of the low pressure exhaust gas recirculation system 150 is provided downstream of the exhaust gas heat exchanger 111 to control the volume of exhaust gas flowing through the exhaust gas heat exchanger 111 or through a bypass passage 113. An exhaust gas recirculation control valve 84 controls the flow of recirculating exhaust gas through the exhaust gas recirculation system 150.
The exhaust gas exiting the compressor 80 passes through an intercooler 83 before entering the engine 105 via an inlet manifold 103.
There are a number of disadvantages with such a system, firstly the arrangement of the exhaust gas heat exchanger 111 and bypass passage 113 are expensive to produce and are difficult to package in the confined space of a modern motor vehicle. Secondly, at certain periods during the operating cycle of the engine 105, such as warm-up from cold, the exhaust gas flowing through the exhaust gas heat exchanger 111 will cause condensation to form in the exhaust gas heat exchanger 111. If this condensate builds up in the exhaust gas heat exchanger 111 there is the possibility that some of it will be dragged by the fast flowing exhaust gas through the conduit joining the catalyst 112 to the compressor 80 thereby risking the ingestion of condensation droplets by the compressor 80. Such ingestion is disadvantageous as it can result in damage to the compressor 80 or to the engine 105. Also the impingement of water droplets in the form of the entrained condensate against the blades of the compressor is likely to reduce its service life even if instantaneous damage does not occur. It is unlikely that any condensate collected in the cooler 111 can flow into the exhaust pipe 107d thereby allowing it to be harmlessly disposed of because such a flow is against the general flow through the low pressure exhaust gas recirculation system.
It is an object of this disclosure to provide a heat exchanger that is of a compact design and is economical to manufacture that can recuperate waste heat for use in heating a cabin of a motor vehicle while also providing cooled exhaust gas for use in a Low Pressure Exhaust Gas Recirculation system.
According to the present disclosure there is provided a combined cabin heater and low pressure exhaust gas recirculation heat exchanger for a motor vehicle comprising an exhaust gas inlet, a coolant inlet connected to a supply of coolant, a coolant outlet connected to a vehicle system, an exhaust gas tapping connected to at least one exhaust gas transfer passage within the heat exchange for supplying exhaust gas to a low pressure exhaust gas recirculation system, and an exhaust gas control valve to vary the flow of exhaust gas through the heat exchange unit. The combined cabin heater and low pressure exhaust gas recirculation heat exchanger may be provided within a combined emissions control device and heat exchanger assembly that has an exhaust gas inlet, receiving exhaust gas from an engine of the motor vehicle, and an exhaust gas outlet connected to the heat exchange unit directing exhaust gas flow to atmosphere.
The present disclosure will now be described by way of example with reference to the accompanying figures.